DNA REPLICATION

1. DNA REPLICATION
Prepared by ,
NAVEENA GIRISH
STUDENT OF CENTRAL UNIVERSITY OF KERALA
KASARAGOD

3. REQUREMENTS -dNTPs , template enzymes, proteins
3’ oh end , primer ,mg2+
DNA REPLICATION IS A SEMI CONCERVATIVE SYNTHESIS
OF DAUGHTER STRAND,EACH PARENTAL STRAND
SERVES AS TEMPLATE

4. Previous 3 models
concer
vative
• Original fully
concerved
dispers
ive
• Fragmented
and old and
new one
mixed
Semi
concerva
tive
• Each strand
template
• Widely
accepted

5. Meselson and stahl

6. Semi concervative -evidence

8. Models of replication
model DNA
templat
e
Breakag
e of
strand
Number of
replicons
Uni/bidirec
tional
e.g. products
theta no 1 Uni/bi Bacteria
Rolling
circle
yes 1 uni virus,F
Linear
eukaryotic
yes many Bidirectional eukaryot
ic

12. DNA POLYMERASE
 ARTHUR KONBERG-ECOLI
 ACTUALLY DOES REPAIR –KONBERG ENZYME
 HELP TO ELONGATE DNA STRAND
 IT CAN POLYMERASE 5’-3’ DIRECTION
 ONLY ADD IN PRESENCE OF PRIMER

13. PROKARYOTIC POLYMERASE
 POLYMERASE ш IMP
 1ST ,2ND AND 3RD

14. EUKARYOTIC POLYMERASE
others –repair and recombination
IN MITOCHONDRIAL
DNA REPLICATION
in nuclear AND
PRIMASE ACTIVITY
IN NUCLEAR,
IN LAGGING STRAND
NUCLEAR , LEADING STRAND
REPLICATION

15.  High fidelity- high specific active sites and repair
mechanism
 Escaped errors –leads to mutation
 Proof reading
 Mismatch repair

19. REPLICATION FORK

20.  Replication fork – point of unwinding and active DNA
synthesis
 Experiment- Ecoli - john cairns -RADIOACTIVE –
THYMIDINE-autoradiography-replication bubble -2
replication forks
 Replication happens in the direction of unwinding
 5’-3’ direction –leading strand
 3’-5’ –lagging strand-composed of okazaki fragments
 -Reiji okazaki discovered it

21. Prokaryotic DNA replication
 INITIATION AND UNWINDING
 ONLY 1 ORI
 INTIATOR PROTEIN JUST UNWIND
 HELICASE- UNWINDING ENZYME

22. HELICASE BIND LAGGING STRAND –
MOVE 5’ TO3’ BY BREAKING H BOND
SSB PROTEINS –PREVENT SUPER
COILING AND REVERSIONING
DNA GYRASE-TOPOISOMERASE –
REDUCE TORQUE( 1st and 2nd )
PRIMASE+ HELICASE=COMPLEX
PRIMING ACTIVITY AND UNWINDING

23. ELONGATION AND TERMINATION
SLIDING CLAMB AND CLAMB LOADING PROTEIN
BOUND ; POLYMERISEш- ELONGATION AND
EXONUCLEASE ACTIVITY
B POLYPEPTIDE CLAMP HELP TO ATTACH TO
TEMPLATE
DNA POLYMERASE 1 - EXO NUCLEASE ,REMOVE
PRIMERS
DNA POLYMERASE 2,4,5 DNA REPAIR

24. DNA
POLYMERASE
5’-3’
POLYMERI
ZATION
3’-5’ EXO
NUCLEASE
5’-3’ EXO
NUCLEASE
FUNCTION
Ì YES YES YES REPLACE
PRIMER
2 YES YES NO DNA REPAIR
3 YES YES NO ELONGATES
DNA
4 YES NO NO DNA REPAIR
5 YES NO NO DNA REPAIR

26.  DNA LIGASE – JOINS OKAZAKI FRAGMENTS BY
NICKS
 TERMINATION- 2FORKS MEET/TERMINATION
PROTEIN BIND TO HELICASE
 PROOF READING 3’-5’ direction
 MIS MATCH REPAIR

27. Eukaryotic replication
DNA polymerase activity
Helicase , topoisomerase, replication protein A bind
Replication licensing factor - mini chromosome maintenance –bind
A multiprotein origin-recognition complex binds to initiate the unwinding of the DNA
They are autonomously replicating sequences( AT) rich
Many ORIGIN OF REPLICATION
Linear and large genome

28.  After DNA Replication ,new nucleosomes
reassemble on the DNA quickly
 Nucleosomes apparently break
 Reassemble from a random mixture of old and
new histones
 Location of replication –replication factories

31. TELOMERASE
LINEAR GENOME FACES GAP AT IT S END AFTER REMOVING
THE PRIMERS
RESPONSIBLE FOR AGING
PROTEIN RNA
TELOMER
ASE
ENZYME

32.  RNA PART 15-20 NUCLEOTIDES
 IT EXTENDS PROTRUDING STRAND
 PRIMER REMOVES AND GAP IS FILLED
BY ALPHA- POLYMERASE / TELOMERES
FOLD BACK FOR UNCONVENTIONAL
BASE PAIRING

34. REPLICATION AND CELLCYCLE
 PROKARYITE –CONTINUOS
 EUKARYOTE –AFTER G1 –IN S PHASE
 LICENCING SYSTEM RESTRICT REPLICATION
AFTER THAT

36. THANK YOU